Description of the Related Art
Regioregular poly(3-hexylthiophene) (RR-P3HT) has received considerable attention in the literature as a semiconducting (conjugated) polymer with relatively high field effect mobility. Measurements of RR-P3HT field effect transistors (FETs) (SiO2 as gate insulator) at room-temperature yielded mobilities of μ=0.045 cm2s−1V−1 (See reference 1) with “bottom-contact” structure, and μ=0.1 cm2s−1V−1 (See reference 2) with “top-contact” structure were reported. The higher mobility was attributed to ordered microcrystalline polymer regions with a lamellar structure formed by self-organization.
The RR-P3HT films used for fabricating the FETs have been deposited by a variety methods with the goal of low cost manufacturing, including, drop casting (See reference 1); spin coating (See references 2-3); printing (See reference 4); and Langmuir-Blodgett (LB) film deposition (See reference 5).
The quality of the RR-P3HT FETs appears to be sensitive to the dynamic self-organization of the macromolecules as the polymer solution passes from the liquid phase to the solid-state phase. A number of external factors can affect the degree of order of the lamellar structure in the microcrystalline regions in the film. For example, RR-P3HT FETs fabricated by drop-casting exhibit higher field-effect mobility than those fabricated by spin-coating. (See reference 1). In the “bottom-contact” FET, the non-flat surface of the substrate (due to the pre-deposited source and drain electrodes) seems to inhibit the structural ordering of RR-P3HT chains during film formation, as evidenced from the observation of higher mobility in “top-contact” FETs (See reference 2).
The major barrier to progress is that most organic polymer FETs have relatively low field mobilities and/or are difficult to synthesize. Inexpensive methods like processing from solution previously yielded poorly ordered films, resulting in low mobilities.
References
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